1. Field of the Invention
An aspect of the present invention relates to a fixing apparatus that fixes, on a recording medium, a toner image that has been transferred to the recording medium by an electrophotographic method, as well as to an image forming apparatus using it.
2. Description of the Related Art
The fixing roller of the fixing apparatus that fixes a toner image on a recording medium is generally classified into a roller having an outermost layer made of silicone rubber and a roller having an outermost layer made of fluororesin (PFA (tetrafluoroethylene-perfluoroalkylvinylether copolymer), PTFE (polytetrafluoroethylene), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), or the like).
In the former roller, the rubber layer comes into contact with a toner image that has been transferred to a recording medium and heating is performed while the rubber layer is deformed elastically following the asperity of the toner image. Therefore, the toner image is not pressed excessively. As such, the former roller is considered advantageous over the latter roller in terms of improvement of image quality. On the other hand, the former roller has drawbacks that it is inferior to the latter roller in durability, heat resistance, and oil resistance.
For low-speed printers which performs printings of tens pages per minute and medium-speed printers which performs printings of about 100 pages per minute, a fixing roller in which a fluororesin layer is formed on a silicone rubber layer and which thus has the advantages of both kinds of rollers has been put in practical use (JP-A-2006-18075).
However, the above-described fixing roller in which the fluororesin layer is formed on the silicone rubber layer is not suitable for practical use in high-speed or ultrahigh-speed printers which performs printings of more than 200 pages per minute because the fluororesin layer on the silicone rubber layer is worn early. Furthermore, fixing rollers used in low-speed and middle-speed printers are so small in diameter as to provide a sufficient nip width of a heat roller and a pressure roller and hence cannot be used as they are in high-speed or ultrahigh-speed printers.